1. Field of the Invention
The present invention relates to a phase difference measuring device especially one which is used in measuring a signal shifting phase when it jitters.
2. Description of the Prior Art
A conventional signal jittering indicator as shown in FIG. 5 comprises a phase detector 50, a low-pass filter/voltage controlled oscillator 60, and an analog-to-digital converter 70. An under-test signal is first sent into the phase detector 50 and a phase difference is outputted from the phase detector 50. The low-pass filter/voltage controlled oscillator 60 receives the phase difference signal and outputs a reference frequency signal. The reference frequency signal is fed back to the phase detector 50 and compared with the under-test signal, in the meanwhile the phase difference signal is sent to the analog-to-digital converter 70 and is converted into a digital signal as an indication of the shifted phase of the undertest signal. A signal wandering indicator is similar to the signal jittering indicator except that a reference frequency signal is provided externally. Both the signal jittering indicator and the signal wandering indicator require an analog-to-digital converter which may be very complicated and high in cost when the indicator is a very high precision indicator. It is known that for a relatively high precision indicator, the converted bit number for each signal cycle is relatively great thus requiring a relatively complicated analog-to-digital converter.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional signal jittering indicator.